The door does not lock. It opens inward. The bookshelves would make a good barricade, but they are bolted in place. I am wearing a leather belt. I am not wearing flip-flops.

This is important data. It could determine whether I will live or die.

We have retreated to the Rainbow Lounge in the Center for Student Diversity at Maryland’s Towson University, normally a safe space for students to celebrate their identity. Today we are asked to imagine that it’s under attack.

An “active shooter” is headed this way.

“If you hear the shots, don’t deny something bad might be happening,” Cpl. Joseph Gregory of the Towson campus police advises the assembled staff. They ask detailed questions about different courses of action. I’m tagging along to get answers to my own questions about the hold mass shootings have taken on America, and what the effect has been.

“You’re trying to buy that three minutes until the police get here,” Gregory says.

Learning to process threats quickly — Gunshots? Construction noise? — is vital. It’s difficult because “freeze mode,” as Gregory calls it, is such an understandable paralysis. When horror erupts amid the routine, the mind wants to explain it away.

Once we accept that the threat is real, we must start to breathe in a special way, or the paralysis of denial will be replaced by the paralysis of panic. It’s physiological, Gregory explains. As our pulse races to 120 beats per minute, we will begin to lose fine motor skills — the ability to fit a key into a lock, say. For a time, fear will enhance our gross motor skills — good for physical exertion. But as our pulse gallops faster, we’ll have trouble thinking. We’ll develop tunnel vision. We’ll lose the ability to interpret sound or react in any way. Soon we’ll be helpless. Then we’ll be murdered.

The diversity center is a suite of offices, conference rooms and lounges, most of which do lock. The outer door is glass and is kept unlocked in accordance with the welcoming spirit of the center.

But what if we’re caught in the Rainbow Lounge, which doesn’t lock? Gregory demonstrates how to stand to the side of the door and wrap your belt around the handle to keep it shut, though this works best if the door opens outward. If the door opens inward, “Flip-flops are great for improvised door jams,” he says.

As a last resort, we must convert our fear into anger. We must swarm the attacker, swinging laptops, coffee mugs, scissors.

“Work as a team,” Gregory says. “It might not be perfect. I’m not going to say the shooter might not get off a round or two.”

When the lesson ends, the staff makes a to-do list — get a lock for the lounge, test the speakers for receiving campus alerts — and briskly returns to work.

An April 1999 photo shows a woman standing among 15 crosses posted on a hill above Columbine High School in Littleton, Colo., where two students killed 13 people and themselves. (Eric Gay/Associated Press)

The siege of the Rainbow Lounge took place after the Pulse nightclub massacre in Orlando, in June, but before the Macy’s rampage north of Seattle, in September, and the only remarkable thing about studying how to defend against a killer in such a mundane environment was how unremarkable it was.

Something has happened to us. Like moviegoers acquainted with the ruse built into the opening scenes of scary films — so many likable characters, only some of whom will survive — we are getting used to conceiving of the most quotidian spaces as potential kill zones. A year ago this week, a married couple killed 14 county workers gathered at the Inland Regional Center in San Bernardino, Calif.

It’s almost as if a cubicle, a sales counter, a blackboard or a popcorn machine could signify the front line of a new war.

But we do not capitulate. As with so many changes and challenges from our history, we innovate and begin to adapt. We make lists, do drills, come up with plans. We may not abolish the horror, but if we factor it into our contingencies, we can tame it and hopefully reduce the death toll.

What gained urgency after Columbine (1999) and Virginia Tech (2007) as specialized tactics for police has been modified into slide presentations conveying best practices for civilians. Hundreds of thousands of adults have received training of one sort or another through federal, local, corporate or educational institutions. Schoolchildren get mandatory “lockdown” drills — lights out, shades drawn, retreat behind the teacher’s desk — which is a gentler name for age-appropriate precautions against someone trying to shoot them.

Every era has its own terrors. Once we practiced civil defense drills, sitting in hallways with no windows in hopes of surviving a nuclear bomb. Now we feel better about the bomb, but it makes perfect sense for poll workers in Denver to have been given active-shooter training for the presidential election. Many of the places where we work and shop are redrafting emergency preparedness protocols to place active shooters on a par with fires, earthquakes, hurricanes and other threats to the continuity of operations. The latest human resources innovation is combat medical tips for the workplace: CPR is useless when an active shooter strikes, but handiness with a tourniquet can save lives.

Yet the live-or-die training boom is just one aspect of a seismic shift in outlook we’re all undergoing in response to this latest killer on the loose.

(Illustration by Jeff Östberg /For The Washington Post)

When did we start calling him “active shooter”?

In 2000, the phrase appeared 17 times in the Nexis database of English-language news sources. In 2010, it was 915 times. Last year, 11,214 times. (“Mass shooting” is similarly trending.)

Fear him or shrug him off, we’ve all thought about him, even though, unlike most killers, we can’t picture him because he fits no profile except for almost always being a man. He strikes anywhere — work, school, mall, movie theater. City, suburb, countryside. The places we know best, our daily havens.

This killer is after just one thing: “A body count,” says one expert.

Another says he “flows like water”: He shoots his way along a path of least resistance — which is why even a door stuck with flip-flops might channel him onward.

Every time there’s an attack, we picture ourselves in that same club, department store or classroom. We see what worked and what didn’t for those people, and we run scenarios. These are our mental active-shooter drills.

Given that most of us will never face an active shooter, his rise to prominence is more about us than him. He’s the perfect nightmare, an avatar of the minute-to-minute possibility of terrorism ripping the facade off the familiar.

Can we do what it takes to be ready without letting him haunt our lives?

People attend a vigil in the wake of the shooting at Pulse nightclub, in Orlando, Fla., where 49 people were killed in June. (Melissa Lyttle/For The Washington Post)

We are not entirely under a hysterical media-induced spell. By some measures, active-shooter attacks really are on the rise.

Grant Duwe, author of “Mass Murder in the United States,” has counted 181 mass public shootings with at least four fatalities since 1900. There were 30 through 1965. Since 1965 there have been 151, including 64 in the past 16 years. The reasons for the increase over the long period aren’t clear. Social upheaval and more alienated, underemployed men could be factors. There may also be a copycat effect. In recent years, controlling for population growth, the rate of increase has leveled off, according to Duwe.

An archetype of the modern active shooter was former Marine sharpshooter Charles Whitman, who picked off passersby from the tower of the University of Texas at Austin in 1966, killing 14. During the 1980s, a cluster of workplace killings — not just at post offices, though this was the age of “going postal” — launched a flurry of trend stories on “the middle-aged berserker, seething with occupational resentment and bent on revenge.”

By then, the Everyman active shooter was expanding his portfolio to more everyday locations, including the slaughter of 21 at a McDonald’s in San Ysidro, Calif., in 1984, and the slaying of 23 at a Luby’s Cafeteria in Killeen, Tex., in 1991. For those of us watching, he was getting closer to home.

Mother Jones’s database of mass public shootings has logged 84 since 1982 in which at least four people were killed (or at least three starting in 2013, when the definition of mass shooting changed).

50 years of U.S. mass shootings: The victims, sites, killers and weapons

The FBI and researchers from Texas State University counted 200 cases from 2000 to 2015, irrespective of the number of fatalities. Peak years were 2009 (19 attacks), 2010 (26), 2012 (21), 2014 and 2015 (20 each). The first eight years averaged seven attacks per year; the second eight averaged 18. There were 1,274 casualties in all, including 578 killed.

And yet, the annual carnage — 90 deaths in 2012, a peak year — is minuscule compared with total gun homicides of about 11,000 a year.

So is our preoccupation with active shooters reasonable?

Consider another threat: the school fire. Deaths are exceedingly rare. More children have been shot to death than burned to death at school in the past two decades. Still, we’d never consider canceling school fire drills, would we?

The outsized impact of mass shootings emanates from the sheer ordinariness of their circumstances. The cliched stammer of witnesses — “We never thought something like this could happen here” — is the moan of illusions being lost.

Who the shooter is matters less than who the victims are and where they died, says Jonathan S. Comer, professor of psychology and director of the Mental Health Interventions and Technology Program at Florida International University in Miami, who studied the psychological impact of the 9/11 attacks and the Boston Marathon bombing.

“One of the best predictors of extended difficulty coping is how much the viewer identifies with the victim,” Comer says. “When large numbers of viewers see events happening at places they could imagine they would be at — they might be at a mall just like that, a family gathering, a marathon — that identification accentuates the emotional connection and makes it more compelling and concerning.”

(Illustration by Jeff Östberg /For The Washington Post)

We do our best to meet this new reality on our own terms. The active-shooter response movement is driven by people like Daniel Nietzel, who calls himself a “child of Columbine.” He was an eighth-grader in Muscatine, Iowa, watching coverage of the mass murder on television until his mother made him turn it off. He told her he wished he were at Columbine “to help.”

He became a teacher and in 2013 found himself in an active-shooter training at West Middle School in Muscatine. Many of the doors could be locked only by going out to the hallway, turning a key in the lock, then ducking back inside.

The trainer made it clear the hallway was no place to be when an active shooter was on the prowl, and it was questionable whether anyone would have the fine motor skills to work a key, or the mental clarity to remember whether the door was already locked.

So, in the drill, Nietzel and some fellow teachers tied their door closed with computer cords. The trainer pushed his way in, pointed at each one and said, “You’re dead, you’re dead, you’re dead.”

“Everyone was pretty upset,” Nietzel recalls.

There wasn’t money to install new locks on all the school’s doors, according to Nietzel. He pondered the problem. Memories of Columbine made him security conscious, attentive to strange noises; he had noticed that after the shootings at an elementary school in Newtown, Conn., in 2012, his students could be startled by a loud locker slam. They were children of Sandy Hook.

One night after grading papers, he cut shapes out of a rubber kitchen container. He showed his colleagues. His next-door neighbor, a metal fabricator, made prototypes.

Nietzel formed a company called Fighting Chance Solutions, along with the school principal, vice principal, guidance counselor, art teacher and his neighbor. Their product: the Sleeve.

The Sleeve is a narrow sheath of steel designed to fit over the closer arms found near the top of many institutional doors. When the Sleeve is in place, the door won’t budge.

The day the company launched in June 2014, there was a shooting at a high school in Oregon.

Now thousands of Sleeves have been sold to universities, Fortune 500 companies and every branch of the military, according to Nietzel. One costs $79; bulk orders get a discount.

The Sleeve (and now the Rampart, also by Fighting Chance Solutions, to barricade a type of door not susceptible to the Sleeve) is part of a growing industry to help defend us from active shooters. Door barricades are just the beginning. LiveSafe is a free app that allows patrons and employees of malls, universities and other locales to share security alerts. First aid “active shooter kits” with tourniquets, seals for sucking chest wounds and “Israeli bandages” that apply pressure by themselves cost $89.99.

“I know there’s a narrative that ‘You guys are profiting off fear, off very unfortunate events,’ ” says Nietzel. “That was never the intention. The intention was to keep my [school] kids safe. Do you say that about door-lock companies?

“To know that something you developed from your head was giving somebody safety and comfort in probably the scariest moment of their life is the culmination of our work.”

A sign posted at a memorial across the street from the Century 16 movie theater in Aurora, Colo., the day after a gunman killed 12 people there in July 2012. (Chip Somodevilla/Getty Images)

We are the first responders now — those of us with no badge, no training, no weapon and, frankly, not much of a workout program.

In my time attending all manner of active-shooter classes, earning certificates of achievement from the Federal Emergency Management Agency and the Department of Homeland Security, I kept meeting police trainers who confessed how strange this feels. Here they were coaching the public to take care of itself. They always thought protecting the public was their job, the reason they got into law enforcement, not something they would outsource back to the public.

The reason they must lies in that three-minutes statistic that Cpl. Gregory mentioned at Towson, where 2,300 people have been trained so far and where, by the way, the door to the Rainbow Lounge now locks. Three minutes is an estimate of the average time it takes police to arrive at an active-shooter scene. Until then, you’re trying to run out the clock.

More than half the incidents end before police intervene; the shooter commits suicide, or he can’t find any more victims because the living have scattered, or, in nearly one in five cases, because potential victims — usually unarmed — act against the shooter, says J. Pete Blair, executive director of Advanced Law Enforcement Rapid Response Training (ALERRT) at Texas State University, a leading purveyor of active-shooter response research and training.

“What we see in the data is that what people do at the attack site is critical,” Blair says. “Actions they take can save their lives, or save the lives of others.”

Fighting the shooter is the last resort. ALERRT preaches a mantra dubbed Avoid Deny Defend: First try to avoid the shooter. If you can’t, then deny him access to your location. If that doesn’t work, defend yourself.

The Department of Homeland Security and some police forces advocate a rival slogan called “Run, Hide, Fight.” Homeland Security coaches companies and schools on how to make active shooter response plans and has trained more than 700,000 people inside and outside the federal government in workshops and on-line courses, says Caitlin Durkovich, assistant secretary for infrastructure protection.

At a church in Salisbury one evening, Cpl. Ted Antal and Trooper First Class Stephen Hallman of the Maryland State Police teach Avoid Deny Defend to about three dozen members of the community. The pair are evangelists of active-shooter response training, sometimes working on their own time. They’ve converted about 2,000 people on the Eastern Shore to new security consciousness in the past year.

“Do you have the knowledge base to stay alive until law enforcement gets there?” Hallman asks the group. “We are coming, but we’re not going to be there at the beginning.”

When police do arrive, they’ll step right over the wounded on the hunt for the shooter. Since it will be a while before medical technicians are cleared to enter, Hallman shows how to use a tourniquet. He mentions that when his daughter is old enough for school, he will send her with a tourniquet in her backpack. He also says he carries a plastic baggy in his wallet, for sucking chest wounds, in case he is ever without his first aid kit.

“Knowledge diminishes fear,” Hallman tells me afterward, explaining a subtler purpose for these classes, beyond the practical tips. “Knowledge helps us understand how not to be afraid. My goal is for this to be such an educated community that it’s not a good target for an active shooter. That’s an idealistic view, but in my mind that’s what drives me.”

Mourners gather at Virginia Tech for a candlelight vigil a day after a student killed 32 people on the campus in Blacksburg, Va., in April 2007. (Evan Vucci/Associated Press)

“Almost like an ax being taken to a piece of wood. It felt like a very quick chop, chop, chop.”

Her French teacher opened the unlockable classroom door to see what was happening, shut it and said to call 9-1-1.

“The last thing I see is two students at the front of the classroom with their arms extended. I think they’re trying to help Madame push their desks to get to the door. But literally as they push — he walks in. He shot them first.”

Anderson’s class was one of the first Seung Hui Cho entered. The students had no time to avoid, deny or defend — a rubric they would not have known anyway.

Two years passed before Anderson spoke publicly about what happened that April 2007 morning in Room 211 of Norris Hall at Virginia Tech. Now she gives presentations across the country:

“He goes down the people one by one by one. It is very quick, it feels very methodical, it feels very intentional. For a few seconds I thought it was a prank. I thought someone might pop out and say, ‘Okay, it’s all over.’ Because your mind tries to put words and logic and meaning around what could be happening. And we didn’t have words for someone who’s shooting in my French class. ... And I thought, Your turn is going to come.”

Anderson was kneeling with her torso on the chair of her combination desk-chair unit, with her hands over her head. The first bullet hit her in the back.

The shooter departed for other classrooms, where in some cases barricades saved lives, and students leapt from second-story windows. He returned to Anderson’s room.

“The second time, you could tell he was looking to see who was alive. There was more time between shots.”

He shot her in the buttocks. A ricochet also hit her toe. Ultimately, a few feet away, he killed himself.

Eleven French students and the teacher were slain in Room 211. In all, 32 students and faculty were killed.

Anderson, now 29, was a sophomore. With surgery, physical therapy and counseling, she graduated on time.

At first, “I didn’t see the value of me retelling what I think of as the worst day of my life,” she told me. That changed when she began to understand the effect her experience had on listeners. Hers is more than a tragic tale or a motivational speech. Anderson has journeyed to the center of the nightmare and returned with hard information.

Her voice has become one of the most compelling in the active-shooter response movement, through her Koshka Foundation, which provides education on the personal and institutional responsibility to prevent, respond to and recover from violence.

“I have an unfortunate advantage in that people are usually interested to know what happened during the Virginia Tech shooting,” she said.

A video of Anderson speaking is part of the curriculum of several active-shooter response trainings I attended before I met her in person. We went to a coffee shop near Burlington, N.J., where the state department of education had invited her to give two presentations, one at a symposium for K-through-12 school administrators and law enforcement, the other open to the public.

She picked a table in a corner. She knows that being shot and watching friends die changed her, but she doesn’t feel as though she walks under a shadow. She thinks she just might see life a little more clearly. She was explaining this when there was a sudden loud bang from the kitchen. She paused.

“Like, I noticed that noise,” she said. “I wouldn’t have noticed that noise before.”

I hadn’t heard it, but it is clear on my digital recorder.

She returned to the conversation, unfazed. She struck me not as a nervous person, but as a highly observant one.

“You feel like your bubble’s been burst,” she said. “The perspective I take is I feel very fortunate because I feel like the gift I’ve received is the gift that most people don’t receive until they’re much older, or until they have some unfortunate disease and they realize they might lose someone in 10 days or 10 months.”

The gift is a profound sense of mortality, which is inseparable from its opposite, a powerful appreciation for life. That’s the note she ends her speeches on.

“Wherever I go, whatever I do, I’m vigilant, and I’m cautious,” she said. “Like right now, you like to sit with your back toward the wall, to be able to view things, and I’m constantly scanning. ... But the other belief I have is that people are good. And until someone gives you a reason not to trust them, you don’t overreact, you don’t overgeneralize, you don’t profile. You lead with the fact that they’re good.”

That evening, more than 100 people came to a high school auditorium to hear Anderson give a presentation titled “Safety Is Personal: Lessons Learned as a Survivor of the Virginia Tech Tragedy.”

Her talks give us permission not to feel sorry for her. And not to be afraid.

She speaks of situational awareness and urges institutions to create “threat assessment teams” to field tips about threatening behavior or nascent plans for violence.

Most of all, she’s trying to show us by example how to discuss these situations, because, she insists, such conversations should be normal.

“If we have the conversations, we’ll be at least mentally preparing,” she said in the coffee shop. “And then if something still does happen, a person feels less victimized because hopefully they took actions to minimize how bad it could have been.”

(Illustration by Jeff Östberg/For The Washington Post)

At Maryland’s Mall in Columbia, the crowded food court is bathed in vapors of soy sauce, grilled onions and fried potatoes.

It feels like the inspiration for the opening of one of those enormously popular active-shooter scenario videos posted on YouTube by police trainers, the banal tranquility before the soundtrack turns ominous and someone starts spraying the premises with semiautomatic gunfire.

Upstairs from the food court is the Zumiez skate shop where, in January 2014, an active shooter assembled a 12-guage shotgun in the dressing room, then killed two employees he apparently did not know before putting the barrel in his mouth and pulling the trigger.

Traces of that tragedy are as subtle as the letters “B” and “T” etched into floor tiles in front of the store for Brianna Benlolo, 21, and Tyler Johnson, 25, the slain employees.

“You want to watch out, but you don’t know what to watch out for,” says Jared Ross, 21, eating Chipotle with two friends. “It could be anyone. It’s not racial; there’s not one specific type of person.”

They grew up hanging out at this mall. After the shooting, for a few months they avoided it. Then, “time passed, we pushed it to the back of our minds,” Ross says. “We do look around more.”

“If I see anyone looking sketchy, I keep my head down, or I just get out,” says Christian Bacote, 21.

Such thoughts can be set aside but not unthought.

“Our attitude is: We’re not going to be afraid,” says Barbara Dawson, 71, who stopped by for milkshakes with her husband, Stephen, 73.

Mornings they walk in the mall for exercise, and the shooting did not deter them.

Stephen Dawson quotes a “Peanuts” cartoon in which Charlie Brown and Snoopy are gazing at a lake.

“Someday, we will all die, Snoopy!”

“True, but on all the other days, we will not.”

Our dual consciousness of active shooters — their lethality and their rarity — may save our lives, but it is also a kind of fall from grace, an unsettling acceptance about the world.

I find a table by myself and order Maryland crab soup from a stand near a mall exit. I note with disapproval that the exit isn’t marked.

The concourse offers open-field sprints in two directions, or possible shelter within one of the shops, if you trust the clerks to control their breathing and manage the security gates.

That banging is the rhythmic striking of a metal spatula on the grill at the Japanese carryout. But if it weren’t, I tell myself, I’d know what to do.

David Montgomery is a staff writer for the magazine. To comment on this story, email wpmagazine@washpost.com or visit washingtonpost.com/magazine.

David MontgomeryDavid Montgomery writes general features, profiles and arts stories for the Washington Post Magazine, including pieces on the Latino community. He joined The Washington Post in 1993 and has covered Prince George’s County, politics in Maryland and life in the District. Follow